problem of balancing consumption with production, touching upon the whole lot of cognate controversial issues which had already been fought out between the schools of Sismondi and Ricardo. Rodbertus' knowledge of crises was of course based upon far more material evidence than that of Sismondi. In his first _Letter on Social Problems_ he already gives a detailed description of the four crises in 1818-19, 1825, 1837-9 and 1847. Since his observations covered a much longer period, Rodbertus could by and large gain a much deeper insight into the essential character of crises than his predecessors. As early as 1850 he formulated the periodical character of the crises which recur at ever shorter intervals and at the same time with ever increasing severity: 'Time after time, these crises have become more terrible in proportion with the increase in wealth, engulfing an ever greater number of victims. The crisis of 1818-19, although even this caused panic in commerce and inspired misgivings in economics, was of small importance compared to that of 1825-6. The first crisis had made such inroads on the capital assets of England that the most famous economists doubted whether complete recovery could ever be made. Yet it was eclipsed by the crisis of 1836-7. The crises of 1839-40 and 1846-7 wrought even greater havoc than previous ones.'--'According to recent experiences, however, the crises recur at ever shorter intervals. There was a lapse of 18 years between the first and the third crisis, of 14 years between the second and the fourth, and of only 12 years between the third and the fifth. Already the signs are multiplying that a new disaster is imminent, though no doubt the events of 1848 put off the catastrophe.'[247] Rodbertus remarks that an extraordinary boom in production and great progress in industrial technique always are the heralds of a crisis. 'Every one of them [of the crises] followed upon a period of outstanding industrial prosperity.'[248] From the crises in history he demonstrates that 'they occur only after a considerable increase of productivity'.[249] Rodbertus opposes what he terms the vulgar view which conceives of crises as mere disturbances in the monetary and credit system, and he criticises the whole of Peel's currency legislation as an error of judgment, arguing the point in detail in his essay _On Commercial Crises and the Mortgage Problem_. There he makes the following comment among others: 'We would therefore deceive ourselves if we were to regard commercial crises merely as crises of the monetary, banking, or credit system. This is only their outer semblance when they first emerge.'[250] Rodbertus also shows a remarkably acute grasp of the part played by foreign trade in the problem of crises. Just like Sismondi, he states the necessity of expansion for capitalist production, but he simultaneously emphasises the fact that the periodical crises are bound to grow in volume.